WoWDB

You can no longer obtain this item from either Gibblewilt (as per Alayea's comment) nor the Big Crate of Salvage. With 7.0.3, Blizzard deleted the Big Crate of Salvage that awarded old world gear (source) with a new crate called Large Crate of Salvage. The new crate only awards garrison resources, materials, weapon/armor enhancements for garrison followers, and (very rarely) pieces of your blue-quality class set (the one that you get if you make a boosted char).

After some looking around, some people speculate you may be able to still get the Foreman Vest from a rarespawn in the old world if it has the old level of Gibblewilt before Cataclysm changed it (thereby letting you tap into a lower level loot table). There have been people who have asked GMs about this item. Although GMs are not allowed to provide direct information on drops (since it's intended to be a kind of hidden thing from players), a couple have implied that it can still drop somewhere else besides either Gibblewilt or the crate, further supporting speculation that another rare may now be able to drop it. I haven't tested this and I can't find mention of anyone who has, and I also don't know